#!/usr/bin/env python
# coding=utf-8

import abc


class Sheep(object):

    # 这一行很重要
    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def get_size(self):
        raise NotImplementedError

if __name__ == "__main__":
    # 创建实例对象时就会失败，而不是等到方法调用才失败
    b = Sheep()
    #b.get_size()

